The objectives of this project are (1) to assess psychophysical methods of experimental pain measurement: (2) to assess clinical pain measures in a dental setting: (3) to use these methods to evaluate underlying mechanisms of clinical pain syndromes; and (4) to evaluate the mechanisms and efficacy of pharmacological and non-pharmacological pain-control agents. The interactive computer-based staircase scaling method was used in five experiments and the continuous track-ball method in two experiments. The first experiment found that 5-weeks of practicing a meditation procedure or spending the same time sitting quietly reduced pain ratings of thermal stimuli in comparison to progressive muscle relaxation or a no treatment control. The second experiment manipulated baroreceptor activity by sitting or reclining postures. No difference was found in pain sensitivity, in contrast to a previous demonstration of analgesia when reclining in comparison to standing. The third experiment assessed the magnitude and fast time course of nitrous oxide analgesia. The results demonstrated the sensitivity of the model, its ability to assess fast kinetics, and the weak potency of nitrous oxide. The fourth experiment provides evidence that cardiac chest pain in patients with normal coronary arteries does not represent general hyperalgesia and is actually accompanied by reduced somatic pain sensitivity. The fifth experiment found that subjects classified as 'defensive' by a paper and pencil test rated thermal stimuli as equally intense but less unpleasant as non-defensive subjects. The sixth experiment found little change in the latency, magnitude or duration of pain responses to thermal stimuli to the hand after an ischemic block that affects both A-beta and A-delta primary afferent fibers. The seventh experiment showed that first and second pain sensation, and their suppression or summation by peripheral or central factors could be adequately evaluated by the track ball method in naive subjects.